This invention relates generally to process control systems and more particularly, but not by way of limitation, to a system for controlling at a well site an apparatus for moving a proppant into a mixing container into which a fluid is flowed for obtaining a blend having a desired concentration of the proppant in the fluid, which blend is to be pumped into the well and which apparatus and mixing container are mounted on a trailer.
Sometimes a process needs to be controlled by a system which can be operated either locally (i.e., near where the process is being performed) or remotely (i.e., spaced from where the process is being performed). Remote control implies the need for some communication means between a local device located near where the process is being performed and a remote device spaced from such location. To facilitate installation and to preclude overly obstructing the area between the local and remote devices, such communication means should be relatively simple and compact; however, such communication means must be capable of handling sufficient quantities and rates of data transmission in both directions between the local and remote devices.
A process control system also often needs to be able to monitor a base or primary characteristic of the process because another characteristic is to be controlled relative to such base or primary characteristic. Feedback from this other, controlled characteristic also needs to be received to determine if the desired control is being obtained.
To provide such a process control system, there is the need for a versatile hardware configuration which can be used to control different processes with little, if any, changes in the hardware being necessary from one process to another. To accomplish this end, the hardware system needs to be designed so that individual parts or sections of the system can be individually programmed to accommodate a specific application. This system should use a simplified communication means by which information can be transferred between the remote and local portions without elaborate interconnections being needed and without overly obstructing the area between the local and remote portions.
By way of example with a specific application, such a control system should be adaptable to control a conventional blender used at a well site to mix a proppant with a fluid to form a fracturing slurry. One known type of conventional blender is a blender trailer manufactured by Halliburton Services. To control such a blender, there need to be parts of the control system adapted to be mounted on the blender trailer and a separate portion adapted to be located remotely from the trailer, such as in a vehicle referred to as a frac van. The parts mountable on the blender trailer should be designed to respond to control signals from the remote part, but the blender-mountable parts should also be capable of implementing local control and even automatic control based on the last received command should there be a loss of communication with the remote control portion. In this specific application, such process control should provide for obtaining and maintaining proper concentrations of proppant relative to the fluid so that the desired slurry is obtained. In a specific implementation, this process control system should allow for variable concentrations to be obtained (e.g., ramp or step changes in concentration). This allows optimally designed fracturing schedules to be implemented more easily than may be accomplished solely through known manual control techniques.